1. Field of the Invention
This invention generally relates to component carriers and more specifically to a system for facilitating the handling of electronic components in integrated circuit packages during the assembly production of electrical circuit assemblies.
2. Description of Related Art
Semiconductor devices have matured from simple circuit elements into complex components provided in a variety of integrated circuit packages. For example, pin grid array (PGA) components have a large number of terminals, can be quite expensive and typically occupy positions on a single circuit board with other PGA components. This maturation has been accompanied by an increase in the complexity of handling these components during assembly and testing operations.
PGA and similar components are more susceptible to damage from a number of external influences, such as mechanical shock and discharges of accumulated electrostatic charge, than were prior components. The consequence of potential damage and other factors has led to changes in transportation, assembly and testing procedures that utilize such components. Indeed, procedures for handling the components now contribute significantly to the success of electronic assembly production.
For example, when electronic components comprised simple transistors, resistors and capacitors, all the components would be assembled on a board without prior testing. If a component failed, simple debugging procedures isolated the defective components for replacement. Now it no longer is economically feasible to replace single PGA and other integrated circuit and similar components if they are mounted on a board. It is easier to discard the entire board with a number of valuable working components than it is to replace a single failed integrated circuit. Thus, present procedures involve component testing prior to assembly to minimize the risk of mounting a defective component. Although this adds costs to the assembly process, overall the added costs are less than those encountered when a board is assembled with a defective component and discarded.
The need to protect and test integrated circuits during assembly operations has led to the development of chip carriers. Chip carriers are special enclosures or packages that house and protect an integrated circuit or the like during processing, production, testing and assembly operations. Over time customers have evolved a number of desirable characteristics for chip carriers. For example, a chip carrier should orient an integrated circuit during the production process and assure proper placement and alignment of terminals for testing and for insertion into a printed circuit board. It should eliminate stresses from the terminals and seals found in such integrated circuits. Chip carriers also should protect a component from mechanical and electrical damage and provide access to all the terminals to facilitate component testing. As the number of circuit designs and packages have proliferated, so have the number of chip carrier configurations. Some of these different chip carrier structures satisfy all of these desirable characteristics necessary for transporting electronic circuits; others satisfy some of them.
In addition to the foregoing, a chip carrier should adapt to automated processing techniques. As a chip carrier transfers along an automated production system, its orientation in space often changes so the chip carrier must include a structure to secure or retain the electronic component in the carrier in a positive manner. However, some mechanisms, such as tooling or fixtures, must insert, remove or reposition such a structure in order to load or unload an integrated circuit component.
The following U.S. Letters Patent are examples of chip carrier structures that have discrete retention structures for securing a component in a chip carrier:
U.S. Pat. No. 4,765,471 (1988) Murphy PA1 U.S. Pat. No. 5,000,697 (1991) Murphy PA1 U.S. Pat. No. 4,615,441 l (1986) Nakamura PA1 U.S. Pat. No. 4,620,632 (1986) Alemanni PA1 U.S. Pat. No. 4,681,221 (1987) Chickanosky et al PA1 U.S. Pat. No. 4,706,161 (1987) Buckingham PA1 U.S. Pat. No. 4,715,835 (1987) Matsuoka
The Murphy-471 patent, that is assigned to the same assignee as the present invention, discloses a chip carrier with an outer frame and a centrally disposed plate having conductive and non-conductive laminations. Apertures through the laminated plate receive PGA terminals and isolate them from each other and the conductive layers of the plate to facilitate testing. The outer frame about the periphery of the plate protects the component and its terminals from mechanical damage. Locking posts at opposite ends of the carrier engage latches on a discrete retainer to secure the retainer plate to the frame. A plurality of cantilevered arms adjacent a central opening through the retainer secure the PGA component against the laminated plates.
In the Murphy-697 patent, that is assigned to the same assignee as the present invention, a PGA carrier has a planar plate for supporting a pin grid array component. A transverse peripheral skirt around the edge of the plate defines upper and lower nested cavities that protect the component housing and the terminal pins respectively. Shock absorbing means extend across one or both of two parallel ends of the peripheral skirt to absorb impact stresses that can occur during transport. The edges of the plate and a removable retaining means have engagement means that secure the retaining means to the carrier. The retaining means overlies the component and secures it in the chip carrier.
The following U. S. Letters Patent describe chip carriers with integrally formed retention devices:
Nakamura discloses a chip carrier with means for supporting an integrated circuit or similar component. A press plate pivots on the carrier to secure the component in the carrier.
Alemanni discloses a chip carrier with separate inserts for supporting differently configured electronic components. Each insert has integral retention fingers with inward projections that overlap the housing. The retention fingers bend outwardly from edges of the housing under application of an external bending force generally in the plane of the carrier. This provides clearance for the insertion of the component. When the fingers are released, they immediately move or relax to normal positions in which flanges on the fingers overlie the component housing and secure it to the carrier insert. Similar retention fingers secure the insert to the chip carrier.
The Chickanosky et al patent discloses a single-piece holder or chip carrier for an electronic component with two flexible over-center snap-acting arms. In a first position the arms open a cavity defined by a peripheral skirt and an internal component support structure. When a component has been deposited on the support structure, the arms are deflected inwardly over center to snap to a second position. In this position the arms overlie the component and secure it in the carrier.
Buckingham discloses a chip carrier with a base member and a cover that pivots on the base member. Various inserts form about the electronic component and lie on the base member. The cover pivots to lock all the inserts to the base member.
Matsuoka discloses a chip carrier with a structure for supporting an electronic component on a base. A cover defines a window for exposing the electronic component to the outside. The cover can snap into a locked position thereby to positively retain the electronic component in the carrier.
These systems can be difficult or cumbersome to utilize in fully automated production lines. In the Murphy-471 patent, for example, the locking posts that secure the retention cover deflect along the axis of motion. It therefore is often necessary to stop chip carrier motion along a production line to release the cover. The Murphy-697 patent discloses a system that is adapted to automated production facilities, particularly for facilitating the removal of the retaining means as the chip carrier moves along a production line, but not the insertion. Further, both systems require handling of the separate retention means.
The Chickanosky patent discloses a system with integral retention means in the form of flexible snap acting arms. However, the chip carrier is dependent upon the size of the component itself and each different carrier has a different outline. Further, arm deflection occurs in the same line as an axis of motion and requires oppositely directed faces. These requirements complicate production. Although the Nakamura, Alemanni, Buckingham and Matsuoka patents disclose carriers that have integral retention means, they also complicate production tooling. For example, the chip carrier shown in the Alemanni patent requires special tooling for spreading four retention fingers simultaneously.